A new study may help explain it. Men who earn significantly less than their female partners, or who earn nothing, are far more likely to cheat than those in relationships where incomes are more or less equal, the study found.

In fact, men who were completely dependent on their partner's income were five times more likely to cheat than men who contributed an equal amount of money to the relationship, according to research presented at the annual meeting of the American Sociological Association.

You’d think such men wouldn’t want to risk their meal ticket. But lower-earning men may be self-medicating their inner macho guy, says Cornell University sociology graduate student Christin Munsch, who conducted the study.

“Having multiple sexual partners may be an attempt to restore gender identity in response to these threats,” she writes. “In other words, for men, sex [outside their relationship] may be an attempt to compensate for feelings of inadequacy with respect to gender identity.”

In fact, says Munsch, we finally have scientific support to the enduring cliché about why any man would drive a Hummer: he’s overcompensating.

But if you’re a woman, here’s the lousy part: “At the other end of the spectrum, those making a lot more are also more likely to cheat,” said Munsch. Men can be bad whether we’re broke or filthy rich.

Does this explain why, say, a guy like singer Benet would not only cheat on Berry but then ask for spousal support during the divorce? Or, conversely, does it explain the uber-famous and rich Tiger’s infatuation with Vegas cocktail waitresses?

Money might not be the issue
Well, maybe, or maybe not. It may not be the money, suggested Christine Whelan, a visiting professor at the University of Pittsburgh and author of “Why Smart Men Marry Smart Women.”

“Money might be a proxy for time away from the spouse,” Whelan said, citing the 2006 Kate Winslet movie “Little Children,” in which a house-husband whose wife is off making documentaries finds companionship at a neighborhood swimming pool with a local stay-at-home mom. On the flip side, when the man is making loads of cash, “you might have a guy working 24/7 cheating on his wife with a secretary or co-worker.”

In case this has sent you scurrying to look at last year’s 1040 forms as if they were marital fortune cookies, “those couples making about the same, or when the men are making a little bit more than the women, appear safest,” Munsch said. She even has a kind of formula: men tend to wander least when their female partner makes 25 percent less than they do.

Munsch's work focused on 18- to 28-year-olds who were married or living together and who had been in the same relationship for at least a year.

Before you go condemning men, though, keep in mind that during the six-year period she studied, 2002 to 2007, less than 7 percent of men “engaged in extradyadic sex” — sounds kinky, but just means they cheated. (More than 3 percent of women cheated, by the way.)

In other words, that’s a small minority. We’re not all quite the rogues you might think. And Munsch pointed out that money was far from the only factor that determined who cheated and who didn’t. Religion, relationship satisfaction, education, and even race played roles, too.

So she’s not arguing that couch potato men, or the guy who’s trying to make a career out of free verse poetry, is a sure bet to stray.

But she does think that male gender roles, and the way they are changing, play a part. “I think American standards of what it means to be a man are a lot to live up to,” she told me. “I think we have a structural problem of how it is defined by every day interactions.” Men who are viewed, or view themselves, as not upholding the male ideal may come to feel inadequate.

Once that happens, it’s either a really big or really fast car, or a nude model with tons of tattoos.